Unwanted page redirection (notably in Safari) - .htaccess

Question

Pages in our 'projects' directory occasionally redirect to the root domain without any input from the user. For example a project here: http://www.mywebsite.com/projects/this-is-the-page/123 will load then redirect to http://www.mywebsite.com - this almost always happens in Safari but not always in other browsers. Usually reloading the original page makes it 'stick' and not redirect. Does this behaviour match anything you've experienced? This site uses the CodeIgniter framework. For your information, our .htaccess file contens is shown below:
RewriteEngine on
RewriteRule ^test.php$ mod_rewrite.php
RewriteCond $1 !^(index\.php|resources|robots\.txt)
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L,QSA]
rewriteCond %{HTTP_HOST} ^mywebsite.cz [NC]
rewriteRule ^(.*)$ http://www.mywebsite.cz/$1 [R=301,L]
rewriteCond %{HTTP_HOST} ^mywebsite.com [NC]
rewriteRule ^(.*)$ http://www.mywebsite.com/$1 [R=301,L]
rewriteCond %{HTTP_HOST} ^mywebsite.eu [NC]
rewriteRule ^(.*)$ http://www.mywebsite.eu/$1 [R=301,L]
AuthName "mywebsite.com"
RewriteCond %{HTTP_HOST} ([^.]+)\.mywebsite.com [NC]
RewriteCond %{HTTP:Accept-Language} (cs) [NC]
RewriteRule ^$ http://www.mywebsite.cz [L,R=301]
RewriteCond %{HTTP_HOST} ([^.]+)\.mywebsite.cz [NC]
RewriteCond %{HTTP:Accept-Language} (cs) [NC]
RewriteRule ^$ /cs/index.php [L,R=301]
RewriteCond %{HTTP_HOST} ([^.]+)\.mywebsite.eu [NC]
RewriteRule ^$ /eu/home [L,R=301]
RewriteCond %{HTTP_HOST} ([^.]+)\.mywebsite.cz [NC]
RewriteCond %{HTTP:Accept-Language} (en) [NC]
RewriteRule ^$ /index.php [L,R=301]
AddType application/vnd.adobe.air-application-installer-package+zip .air
AddType application/x-shockwave-flash .swf
AddType application/x-httpd-php .xml
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/xml
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE text/javascript
AddOutputFilterByType DEFLATE application/x-javascript
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE application/x-httpd-php
# BEGIN Compress text files
<ifModule mod_deflate.c>
<filesMatch "\.(css|js|x?html?|php)$">
SetOutputFilter DEFLATE
</filesMatch>
</ifModule>
# END Compress text files
# BEGIN Expire headers
<ifModule mod_expires.c>
ExpiresActive On
ExpiresDefault "access plus 1 seconds"
ExpiresByType image/x-icon "access plus 2592000 seconds"
ExpiresByType image/jpeg "access plus 2592000 seconds"
ExpiresByType image/png "access plus 2592000 seconds"
ExpiresByType image/gif "access plus 2592000 seconds"
ExpiresByType application/x-shockwave-flash "access plus 2592000 seconds"
ExpiresByType text/css "access plus 604800 seconds"
ExpiresByType text/javascript "access plus 216000 seconds"
ExpiresByType application/javascript "access plus 216000 seconds"
ExpiresByType application/x-javascript "access plus 216000 seconds"
ExpiresByType text/html "access plus 600 seconds"
ExpiresByType application/xhtml+xml "access plus 600 seconds"
</ifModule>
# END Expire headers
# BEGIN Cache-Control Headers
<ifModule mod_headers.c>
<filesMatch "\.(ico|jpe?g|png|gif|swf)$">
Header set Cache-Control "max-age=2592000, public"
</filesMatch>
<filesMatch "\.(css)$">
Header set Cache-Control "max-age=604800, public"
</filesMatch>
<filesMatch "\.(js)$">
Header set Cache-Control "max-age=216000, private"
</filesMatch>
<filesMatch "\.(x?html?|php)$">
Header set Cache-Control "max-age=600, private, must-revalidate"
</filesMatch>
</ifModule>
# END Cache-Control Headers
# BEGIN Turn ETags Off
<ifModule mod_headers.c>
Header unset ETag
</ifModule>
FileETag None
# END Turn ETags Off
# BEGIN Remove Last-Modified Header
<ifModule mod_headers.c>
Header unset Last-Modified
</ifModule>
# END Remove Last-Modified Header